1. Field of the Invention
The invention relates to a wafer lens array and a stack style wafer lens array. The invention also relates to a mold for manufacturing the wafer lens array and an apparatus for manufacturing the wafer lens array. In addition, the invention relates to a method for manufacturing a wafer lens array.
2. Description of the Related Art
Currently, portable terminals of electronic device such as mobile phone and PDAs (Personal Digital Assistant) are equipped with image pickup units which have small and thin shapes.
Such image pickup units generally include a solid-state image pickup device such as a CCD (Charge Coupled Device) image sensor or a CMOS(Complementary Metal-Oxide Semiconductor) image sensor, and lenses that form an image on the solid-state image pickup device. As mobile terminals become smaller and thinner, the image pickup units mounted on those are also required to achieve reduction in size and thickness. In order to decrease the cost of the portable terminals, improvement of productivity is desired. As a method for manufacturing such small lenses in large numbers, known is a method for lenses module comprising producing a wafer lens array comprising a substrate section and a plurality of lenses on the substrate section, cutting the substrate section to form pieces comprising a lens. By the method, lens modules can be mass-produced. Also known is a method for mass-manufacturing an image pickup unit comprising integrally combining a substrate section in which a plurality of lens sections are formed and a sensor substrate in which a plurality of solid-state imaging pickup device was form formed and cutting the sensor substrate with the substrate so that the unit comprises a lens and a solid-state imaging pickup device.
Heretofore, as the references concerning the wafer lens, knows are JP-T-2005-539276, WO07/107,025, JP-A-H7-248404, and JP-A-2003-294912. JP-T-2005-539276 discloses a multilayer-structure comprising stacked wafer lenses which comprise a substrate and a plurality of lenses on the substrate. WO07/107,025 discloses a method comprising feeding formation material on a substrate to form a lens on the substrate using a mold. As is different from the above wafer lens, a known article comprising a plurality of lenses is a micro lens array which does not integrally connect with the substrate. JP-A-H7-248404 does not use a mold for forming lenses since a resin layer which is formed on one side of a substrate is pressed and cured with a substrate comprising holes. JP-A-2003-294912 discloses a technique for forming a micro lens array comprising a two-layer structure, wherein the axes of the two layers adjusted to correspond to each other.
In the production of a wafer lens array composed of resin material, the resin material capable of curing through light or heat is generally cured inside a mold to product a wafer lens array. A plurality of wafer lens arrays is required to be stack to each other at a desired interval, wherein the plurality of wafer lens arrays has each a different shape in the lens section to each other. A method for sticking a plurality of wafer lens arrays to each other at a desired interval is exemplified by a method comprising sandwiching suitably selected gap material such as spacer between wafer lens arrays to adhere to each other, a method for dispersing particles into adhesive, or a method for improving a mechanical accuracy. However, those methods are concerned to increase of the cost due to increase of kinds of member to be used, and to demand of introduction of high-accuracy apparatus.
Therefore, the most desirable is to form gap sections on a wafer lens array itself from the viewpoint of the production cost. FIG. 1 is a schematic view showing a cross-section view perpendicular to the inner edge of the lens section of a conventional wafer lens array with gaps, wherein 1 stands for a lens, 2•2 stands for a substrate which connects the lenses to each other, and 3•3 stands for a gap which projects from the substrate 3 from a direction opposite to the lens 2. Such a wafer lens array with a gap was manufactured by the method shown in FIG. 2. FIG. 2 is a schematic view of methods for manufacturing a wafer lens array, wherein (a) shows a method for manufacturing a wafer lens array not comprising any gaps, and (b) shows a method for manufacturing a wafer lens array comprising gaps on the wafer lens array itself. In those methods, a mold 4 composed of glass, metal, or the like was pushed up to contact with resin 5, the resin was cured, and then, was released by moving the mold down. In the method for manufacturing the wafer lens array without gaps, the mold 4 is pushed up for forming sections corresponding to lenses (FIG. 2 (a)). Contrary to this, when the gaps are formed on the wafer lens array itself, the mold 4 is further pushed up for forming sections corresponding to gaps in addition to the sections corresponding to lenses (FIG. 2 (b)).
As mentioned above, the wafer lens array with gaps can be formed by an almost similar process to the process for manufacturing the wafer lens array without gaps. However, the production process for a wafer lens array with gaps produces a faulty product extremely more frequently, compared with the wafer lens array without gaps. In the case of the wafer lens array with gaps, when the resin is cured, and then, the mold is moved down to release the resin, the wafer lens array may be broken. This is because the resin and the mold each have different contraction percentage, and thereby, the wafer lens array gets hung up to a convex section inside the mold (a section corresponding to lens). In order to prevent the wafer lens array with gaps from being broken, it is demanded that the process is improved for the release of the resin from the mold. As a result, the yield of the wafer lens array with gaps decreases, or the takt time for releasing increases, and therefore, the cost becomes high.
JP-A-2004-151363 discloses a stacked lens array, wherein the lens arrays are bonded to each other by tightly fitting tapered concave portions and convex portions formed on each lens array when the lens arrays are stacked. However, in JP-A-2004-151363, the taper sections are tightly fitted to each other, and, as the result, the lens arrays may be broken or the taper sections may be shaved. When the lens arrays have a large size of surface area, it is difficult to adjust the distances between the individual lens arrays in one plane. That is, there is a problem in that the stacked lens arrays have sections which are completely fitted and sections which are not completely fitted. This causes reduction of properties for a lens unit. On the other hand, JP-A-2004-151363 discloses a resin-molded lens which is characterized by having a tapered shape in which the contour of a circular lens gradually becomes wide. However, JP-A-2004-151363 discloses a method for manufacturing only one lens and is silent to application to wafer lens array having sequentially-positioned lenses.